Phase-matching device for electronic ovens



Sept. 1, 1970 J. E. STAATS 3,526,738

PHASE-MATCHING DEVICE FOR ELECTRONIC OVENS Filed Oct. 17, 1968 INVENTOR JAMES E. STAA rs emf @M M 2? F Arm.

United. States Patent US. Cl. 219-1055 12 Claims ABSTRACT OF THE DISCLOSURE An electronic oven is disclosed including a cooking cavity and a source of high frequency electromangetic wave energy coupled thereto by a coaxial type transmission line of limited physical length, the inner conductor of the transmission line comprising two spaced-apart sections defining therebetween a gap of a predetermined length, and an electrically conductive U-shaped member having a pair of legs respectively connected to the inner conductor sections for bridging the gap therebetween, the distance along said U-shaped member between the inner conductor sections being greater than the predetermined length but not greater than the electrical wave length at the operating frequency of the source.

The present invention relates to electronic or microwave ovens, and especially to transmission lines for coupling a source of high frequency electromagnetic wave energy to a cooking cavity. In particular, this invention relates to phase-matching devices for such transmission lines for phase matching the source to the cooking cavity.

It is an important object of this invention to provide an electronic oven including a common enclosure surrounding a cooking cavity and a generator of high frequency electromagnetic wave energy and a transmission line coupling the generator to the cooking cavity, the common enclosure limiting the physical length of the transmission line, and means for increasing the effective electrical length of the transmission line without changing its physical length for providing phase matching of the generator to the cooking cavity.

It is another object of this invention to provide an electronic oven including a cooking cavity and a generator for generating high frequency electromagnetic wave energy and a transmission line coupling the generator to the cooking cavity and including a hollow outer conductor and an inner conductor, the inner conductor having a gap therein between the generator and the cooking cavity of a first predetermined length, and an electrically conductive member bridging the gap and having a second predetermined length, the second predetermined length exceeding the first predetermined length by a third predetermined length, the third predetermiend length being no greater than one-half of the Wave length of the operating frequency of the generator and being sufficient for providing phase matching of the generator to the cooking cavity.

It is a further object of this invention to provide an electronic oven of the character described wherein the inner conductor of the transmission line includes two Patented Sept. 1, 1970 spaced-apart sections terminating in a pair of spacedapart ends providing a gap therebetween of a first predetermined length, and wherein the bridging member includes an electrically conductive U-shaped member having a pair of legs connected at the outer ends thereof respectively to the inner conductor section ends, the longitudinal axes of the legs being disposed substantially normal to the longitudinal axes of the inner conductor sections, the distance along the U-shaped member between the inner conductor sections being of a second predetermined length which exceeds the first predetermined length by a third predetermined length, the third predetermined length being no greater than one-half of the wave length of the operating frequency of the generator and being suflicient for providing phase matching of the generator to the cooking cavity.

The invention, both as to its organization and method of operation together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accom panying drawing, in which:

FIG. 1 is a view in vertical cross section of an electronic oven constructed in accordance with the present invention;

FIG. 2 is an enlarged fragmentary view in horizontal section taken along the line 22 in FIG. 1; and

FIG. 3 is a view in vertical section along the line 3-3 in FIG. 2.

Referring now to the drawing, and particularly to FIG. 1 thereof, there is shown an electronic oven, designated by the numeral 70, which comprises a cooking cavity 75, a microwave generator 85, a transmission line 90 interconnecting the cooking cavity and the microwave generator 85 and a phase-matching device 100, all disposed within a surrounding common enclosure 95. The cooking cavity 75 is defined by an upstanding substantially boxlike wall structure generally designated by the numeral 71 having substantially the configuration of a rectangular parallelepiped. A front Wall 72 of the wall structure 71 has a doorway 73 therein opening into the cooking cavity 75 defined by the wall structure 71. Further, the front wall 72 is provided with a front door 74 hingedly connected thereto by an associated hinge structure 78 and cooperating with the doorway 73, whereby the door 74 is movable between a substantially vertical closed position and a substantially horizontal open position with respect to the doorway 73 in the wall structure 71. Also, the front door 74 includes a handle 76 and the usual inner foraminous sheet 77 formed of steel which cooperates with wall structure 71 completely to enclose the cooking cavity 75 when the front door 74 occupies its closed position.

Disposed adjacent to and immediately below a top wall 79 of the wall structure 71 is an antenna structure generally designated by the numeral 80. The antenna structure 80 is more fully described in applicants US. Pat. No. 3,221,132 which issued on Nov. 30, 1965. The uniform field provided by the antenna structure 80 is diagrammatically illustrated in FIG. 1 of the drawing by the dashed line which is indicated with the arrows marked with the letter E. The resultant field is substantially uniform throughout a large area disposed centrally of the cooking cavity and uniformly decreases to zero at the outer edges thereof.

A suitable source of microwave energy for use in operating the microwave oven is shown in FIG. 1 of the drawing and is generally designated by the numeral 85. One preferred source of microwave energy is a crossed field electronic discharge device in the form of a multiple cavity magnetron device of the type illustrated and described in applicants US. Pat. No. 3,377,562 which issued on Apr. 9, 1968. The magnetron device described in that patent is particularly well suited for incorporation in electronic cooking apparatus such as the electronic oven 70 of the present invention. More particularly, this magnetron device is designed to oscillate at an ultra-high frequency of about 915 mHz., employing anode-cathode voltages in the general range 250 to 1,000 volts DC. with corresponding RF. power outputs in the general range 80 to 2,400 watts. Specifically, at a plate voltage of about 290 volts DC, this magnetron device has a continuous R.F. power output of about 100 watts at the ultra high frequency of 915 mHz.; at a plate voltage of about 570 volts DC, this magnetron device has a continuous RF. power output of about 700 watts at the ultra high frequency of 915 mHz.; and at a plate voltage of about 1,000 volts DC, this device has a peak RF. power output of about 2,400 watts at the ultra high frequency of 915 mHz.

By using suitable control and power supply systems, which are also described in detail in the aforementioned US. Pat. No. 3,377,562, the above-described magnetron device can be readily operated from the usual household three-wire Edison network of 236 volts single-phase, 60'- cycles AC.

The microwave energy produced by the generator 85 is coupled to the cooking cavity defined within the wall structure 71 by a transmission line generally designated by the numeral 90. The transmission line 90 is preferably of the co-axial type having a hollow outer conductor 92 surrounding an inner conductor 93. The inner conductor 93 may be either hollow or solid, but is preferably hollow, and the outer conductor 92 and the inner conductor 93 may both have either a rectangular or a circular cross section, but preferably each has a circular cross section. The inner conductor 93 extends downwardly through the upper wall 79 of the wall structure 71 and is connected to the antenna structure at an input terminal 94 thereof.

The wall structure 71 and the generator and the transmission line are all enclosed by the common enclosure 95 indicated by broken lines in FIG. 1 of the drawing. The dimensions of the enclosure 95 are determined by commercial requirements such as the dimensions of the overall cabinetry structure into which the electronic oven 70 has to be fitted or with which it is to be used, and these dimensions in turn limit the allowable length of the transmission line 90.

Disposed in the transmission line 90 between the wall structure 71 and the microwave generator 85 is a phasematching device generally designated by the numeral 100, which will now be described in detail. Referring now to FIGS. 2 and 3 of the drawing, the phase-matching device is shown disposed in the transmission line 90. The outer conductor 92 of the transmission line 90 has an opening therein generally designated by the numeral 101. The opening 101 is preferably circular in outline and has a diameter approximately equal to the diameter of the outer conductor 92 of the transmission line 90. Disposed within the opening 101 is an outer conductor section 102 having a cylindrical shape and attached at one end thereof to the outer conductor 92 along the edge of the opening 101 therein. The outer conductor section 102 preferably has a circular cross section of a diameter equal to the diameter of the outer conductor 92 and defines a cylindrical housing which has a longitudinal axis disposed substantially normal to the longitudinal axis of the transmission line 90 and extends outwardly therefrom. The outer end of the outer conductor section 102 is closed by a dust cover 103. Disposed within the outer conductor section 102 intermediate the ends thereof and coaxial therewith is an insulating spacer 104 having a circular outline and having a centrally positioned rectangular opening therethrough.

The inner conductor 93 of the transmission line 90 comprises two sections 105 and 106 terminating respectively in ends 107 and 108, which ends define therebetween a gap having a predetermined length and being generally designated by the numeral 110. An annular insulating spacer 112 is disposed within the outer conductor 92 and around the inner conductor section 105 adjacent to the end 107 thereof. The spacer 112 serves to center the inner conductor section 105 within the outer conductor 92 of the transmission line 90. Similarly, an annular insulating spacer 114 encircles the inner conductor section 106 adjacent to the end 108 thereof for centering the inner conductor section 106 within the outer conductor 92.

A bridging means generally designated by the numeral 115 is connected across the gap in the inner conductor 92. The bridging means is substantially U- shaped and includes a pair of elongated substantially parallel legs 116 and 117 connected at one end by and integral with a connecting portion or bight 118. The longitudinal axes of the legs 116 and 117 are disposed substantially normal to the longitudinal axes of the inner conductor sections 105 and 106. Each of the legs 116 and 117 and the bight 118 have a thin flat strap-like shape rectangular in cross section. The bight 118 of the bridging means 115 is disposed outwardly from the inner conductor 93 beyond the opening 101 in the outer con ductor 92 and in the outer conductor section 102 and beyond the rectangular opening in the insulating spacer 104. The outer end of the outer conductor section 102 extends beyond the bight 118 by a distance at least as great as the difference between the radius of the outer conductor 92 and the radius of the inner conductor 93. The substantially parallel legs 116 and 117 of the bridging means 115 are spaced apart a distance substantially equal to the diameter of the inner conductor 93. The ends of the legs 116 and 117 of the bridging means 115 extend into the gap 110, the free ends of the legs 116 and 117 extending completely across gap 110 to the opposite surface of the inner conductor sections 105 and 106, respectively. The leg 116 abuts the end 107 of the inner conductor section 105 and the leg 117 abuts the end 108 of the inner conductor section 106. Disposed within the gap 110 and between the legs 116 and 117 of the bridging means 115 is an insulating block or plug 119.

The bridging means 115 is coupled to the inner conductor sections 105 and 106 respectively by two threaded bullet couplers each generally designated by the numeral 120. Each of the bullet couplers 120 includes an outer portion 121 having a circular cross section of a diameter substantially equal to the inner diameter of the inner conductor 93. The outer end of the outer portion 121 is tapered slightly inwardly toward the axis thereof, forming a tapered surface 122. A substantially rectangular slot 123 is cut axially into the outer portion 121 from the outer end thereof thereby dividing the outer portion 121 into a pair of prongs that normally have an interend fit with the interior surface of the conductor sections 105 and 106, as the case may be, but which can be resiliently pressed toward one another to permit insertion thereof thereinto. Each of the couplers 120 also includes a threaded inner portion 124 having a circular cross section of a diameter less than the diameter of the outer portion 121. The inner portions 124 of the couplers 120 are respectively fitted through appropriately formed holes in the legs 116 and 117 of the bridging means 115 adjacent to the free ends thereof and are threadedly engaged with the insulating plug 119. The outer portions 121 of the bullet couplers 120 are resiliently friction-fitted, respectively, into the open ends 107 and 108 of the inner conductor sections 105 and 106, thereby coupling the bridging means 115 to each of the inner conductor sections 105 and 106 for bridging the gap 110 therebetween.

In operation, the bridging means 115 serves to increase the electrical length of the transmission line 90 without changing the physical length thereof. This allows for phase matching of the generator 85 to the cooking cavity defined within the wall structure 71 of the electronic oven 70. Thus, when the space limitations imposed by the enclosure 95 do not allow for a proper length of the transmission line 90 for providing a phase match between the generator 85 and the cooking cavity 75, the phase matching device 100 is inserted in the transmission line 90 to alter the effective electrical length thereof by a sufficient amount to achieve the desired phase matching. This is accomplished without increasing the physical length of the transmission line 90 as limited by the enclosure 95.

To achieve the desired electrical results it is necessary that the difference between the length along the bridging means 115 from inner conductor section- 105 to inner conductor section 106 and the length of the gap 110 is no greater than one-half of the wave length at the operating frequency of the microwave generator 85. In particular, it is preferred that this difference be in the range between about one-tenth of the wave length at the operating frequency of the microwave generator 85 and about four-tenths of that wave length.

It can be seen that there has been disclosed an electronic oven including a wall structure 71 defining a cooking cavity therein and a microwave generator 85 for electromagnetic wave energy and a transmission line 90 including an outer conductor 92 and an inner conductor 93 coupling the microwave generator 85 to the cooking cavity 75, wherein the wall structure 71, the microwave generator 85 and the transmission line 90 are all confined within a common enclosure 95. Disposed in the transmission line 90 between the microwave generator 85 and the cooking cavity 75 is a phase-matching device 100 including a U-shaped bridging means 115 having a pair of legs 116 and 117, the longitudinal axes of which are disposed substantially normal to the longitudinal axis of the transmission line 90. The inner conductor 93 includes a pair of sections 105 and 106 terminating respectively in ends 107 and 108 and defining therebetween a gap 110. The legs 116 and 117 are respectively coupled to the inner conductor sections 105 and 106 at the ends 107 and 108 thereof by two threaded bullet couplers 120, the U- shaped bridging means 115 thereby bridging the gap 110 and increasing the effective electrical length of the transmission line 90 without changing the physical length thereof for phase matching the microwave generator 85 to the cooking cavity 75.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

-1. In an electronic oven, structure defining a cooking cavity, a generator for generating high frequency electromagnetic wave energy and having a pair of output terminals, a transmission line coupling said generator to said cooking cavity and including a hollow outer conductor coupled to one terminal of said generator and an inner conductor coupled to the other terminal of said generator, said inner conductor having a gap therein between said generator and said cooking cavity, said gap having a first predetermined length, and an electrically conductive member bridging said gap and having a second predetermined length and a pair of ends, one end of said conductive member being coupled to said inner conductor at one end of said gap and the other end of said conductive member being coupled to said inner conductor at the other end of said gap, said second predetermined length exceeding said first predetermined length by a third predetermined length, said third predetermined length being no greater than one half of the wavelength of the operating frequency of said generator and being sufiicient for providing phase matching of said generator to said cooking cavity, whereby to provide an effective electrical length for said transmission line exceeding the physical length thereof for phase matching said generator to said cooking cavity without changing the physical length of said transmission line.

2. An oven as set forth in claim 1, and further including a common enclosure surrounding said cooking cavity and said generator and said transmission line, said enclosure limiting the physical length of said transmission line.

3. An oven as set forth in claim 1, wherein said inner conductor is hollow.

4. An oven as set forth in claim 1, wherein both said inner conductor and said outer conductor have a circular cross section.

5. An oven as set forth in claim 1, wherein said third predetermined length is no greater than four-tenths of the wave length of the operating frequency of said generator and no less than one-tenth of said wave length.

6. In an electronic oven, structure defining a cooking cavity, a generator for generating high frequency electromagnetic wave energy and having a pair of output terminals, a transmission line coupling said generator to said cooking cavity and including a hollow outer conductor coupled to one terminal of said generator and an inner conductor coupled to the other terminal of said generator, said inner conductor including two spaced-apart sections terminating in a pair of spaced-apart ends providing a gap between said generator and said cooking cavity of a first predetermined length, and a bridging means closing said gap, said bridging means including an electrically conductive U-shaped' member having a pair of legs connected at the outer ends thereof respectively to said inner conductor section ends, the longitudinal axes of said legs being disposed substantially normal to the longitudinal axes of said inner conductor sections, the distance along said U-shaped member between said inner conductor sections being of a second predetermined length, said second predetermined length exceeding said first predetermined length by a third predetermined length, said third predetermined length being no greater than one-half of the wave length of the operating frequency of said generator and being suflicient for providing phase matching of said generator to said cooking cavity, whereby to provide an effective electrical length for said trans mission line exceeding the physical length thereof for phase matching said generator to said cooking cavity without changing the physical length of said transmission line.

7. The oven as set forth in claim 6, wherein said outer conductor has an opening therein accommodating said U-shaped member therethrough and further including an outer conductor section attached to said outer conductor and extending outwardly therefrom and surrounding that portion of said U-shaped member which extends outwardly through said opening beyond said outer conductor.

8. The oven as set forth in claim 7, and further including an insulating member centering said U-shaped member within said outer conductor section.

9. The oven set forth in claim 7, wherein said inner conductor and said outer conductor and said outer conductor section each has a circular cross section, and wherein the ratio of the diameter of said outer conductor to the diameter of said inner conductor is equal to the ratio of the diameter of said outer conductor section to the distance between the legs of said U-shaped member.

10. The oven as set forth in claim 6, wherein said inner conductor section ends are hollow and wherein said coupling means includes a pair of threaded bullet couplers, each of said couplers having an outer portion axially frictionally fitted into the open end of the adjacent one of said inner conductor sections and an inner portion engaging the adjacent leg of said U-shaped member adjacent to the outer end thereof.

11. The oven as set forth in claim 10', further including an insulating member disposed between the legs of said U-shaped member adjacent to the outer ends thereof, said member being threadedly engaged with the inner portion of each of said bullet couplers.

12. The oven as set forth in claim 6, and further including two annular insulating members respectively disposed adjacent to the free end of each of said inner conductor section and centering said inner conductor section within said outer conductor.

References Cited UNITED STATES PATENTS Revercomb et a1. 219-10.55

JOSEPH V. TRUHE, Primary Examiner 10 L. H. BENDER, Assistant Examiner U.S. Cl. X.R. 

